Loneliness is a major risk factor for both psychological disturbance and poor health outcomes in adults. This study aimed to assess whether childhood loneliness is associated with a long-term disruption in mental health that extends into adulthood.

This study is based on the longitudinal, community-representative Great Smoky Mountains Study of 1420 participants. Participants were assessed with the structured Child and Adolescent Psychiatric Assessment interview up to eight times in childhood (ages 9–16; 6674 observations; 1993–2000) for childhood loneliness, associated psychiatric comorbidities and childhood adversities. Participants were followed up four times in adulthood (ages 19, 21, 25, and 30; 4556 observations of 1334 participants; 1999–2015) with the structured Young Adult Psychiatric Assessment Interview for psychiatric anxiety, depression, and substance use outcomes.

Both self and parent-reported childhood loneliness were associated with adult self-reported anxiety and depressive outcomes. The associations remained significant when childhood adversities and psychiatric comorbidities were accounted for. There was no evidence for an association of childhood loneliness with adult substance use disorders. More associations were found between childhood loneliness and adult psychiatric symptoms than with adult diagnostic status.

Childhood loneliness is associated with anxiety and depressive disorders in young adults, suggesting that loneliness – even in childhood – might have long-term costs in terms of mental health. This study underscores the importance of intervening early to prevent loneliness and its sequelae over time.